《java数据结构与算法》笔记-CH4-8栈结构实现后缀表达式计算结果

/**
 * 中缀表达式转换成后缀表达式： 从输入（中缀表达式）中读取的字符，规则： 操作数： 写至输出 左括号： 推其入栈 右括号： 栈非空时重复以下步骤-->
 * 若项不为(,则写至输出； 若项为(，则推出循环 operator(opThis): 若栈为空，推opThis； 否则，重复-->
 * 弹出一项，若项为(,推其入栈； 若项为operator，且 若opTop<opThis,推入opTop,或 若opTop>=opThis,输出opTop,
 * 若opTop<opThis则退出循环，或项为( 推入opThis 没有更多项： 当栈非空时，弹出项目，将其输出
 *
 */
class StackI {
	private int maxSize;
	private char[] stack;
	private int top;

	public StackI(int size) {
		maxSize = size;
		stack = new char[size];
		top = -1;
	}

	public void push(char value) {
		stack[++top] = value;
	}

	public char pop() {
		return stack[top--];
	}

	public char peek() {
		return stack[top];
	}

	public char peekN(int index) {
		return stack[index];
	}

	public int size() {
		return top + 1;
	}

	public boolean isFull() {
		return top == maxSize;
	}

	public boolean isEmpty() {
		return top == -1;
	}

	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder();
		sb.append("[");
		for (int i = 0; i < size(); i++) {
			sb.append(peekN(i) + ",");
		}
		sb.deleteCharAt(sb.length() - 1);
		sb.append("]");
		return sb.toString();
	}

	public void display() {
		System.out.print("当前栈: " + toString());
	}
}

class InToPost {
	private String input, output;
	private StackI stack;

	public InToPost(String in) {
		input = in;
		output = "";
		int stackSize = input.length();
		stack = new StackI(stackSize);
	}

	public void gotOper(char opThis, int prec1) {
		while (!stack.isEmpty()) {
			char opTop = stack.pop();
			if (opTop == '(') {
				stack.push(opTop);
				break;
			} else {
				int prec2;
				if (opTop == '+' || opTop == '-')
					prec2 = 1;
				else
					prec2 = 2;
				if(prec2<prec1){
					stack.push(opTop);
					break;
				}else{
					output += opTop;
				}
			}
		}
		stack.push(opThis);
	}

	public void gotParen(char ch){
		while(!stack.isEmpty()){
			char chx = stack.pop();
			if(chx == '(')
				break;
			else
				output += chx;
		}
	}

	public String doTrans() {
		for (int i = 0; i < input.length(); i++) {
			char ch = input.charAt(i);
			switch (ch) {
			case '+':
			case '-':
				gotOper(ch, 1);
				break;
			case '*':
			case '/':
				gotOper(ch, 2);
				break;
			case '(':
				stack.push(ch);
				break;
			case ')':
				gotParen(ch);
				break;
			default:
				output += ch;
				break;
			}
		}
		while(!stack.isEmpty()){
			output += stack.pop();
		}
		return output;
	}
	/**
	 * 计算后缀表达式结果
	 * 遇到操作数--入栈
	 * 遇到操作符--从栈中提取两个操作数，用操作符执行运算，结果入栈
	 * 注：这里转换后缀和计算后缀表达式共用了一个栈类型Model，所以在计算过程中字符和int转换时多了一些操作
	 * @param in
	 * @return
	 */
	public int doParse(String in){
		stack = new StackI(20);
		int num1,num2,result = 0;
		int j;
		char c;
		for(j=0;j<in.length();j++){
			c = in.charAt(j);
			if(c>='0' && c<='9'){
				stack.push(c);
			}else{
				num2 = (int)(stack.pop()-'0');
				num1 = (int)(stack.pop()-'0');
				switch (c) {
				case '+':
					result = num1+num2;
					break;
				case '-':
					result = num1-num2;
					break;
				case '*':
					result = num1*num2;
					break;
				case '/':
					result = num1/num2;
					break;
				default:
					result = 0;
					break;
				}
				stack.push((char)(result+'0'));
			}
		}
		result = (int)(stack.pop()-'0');
		return result;
	}
}

public class InfixDemo {
	/**
	 * 读取字符串
	 *
	 * @return
	 * @throws IOException
	 */
	public static String getString() throws IOException {
		InputStreamReader isr = new InputStreamReader(System.in);
		BufferedReader reader = new BufferedReader(isr);
		return reader.readLine();
	}
	public static void main(String[] args) throws IOException {
		String input, output;
		while(true){
			System.out.println("enter:");
			System.out.flush();
			input = getString();
			if(input.equals(""))
				break;
			InToPost i = new InToPost(input);
			output = i.doTrans();
			System.out.println(output);
			System.out.println(i.doParse(output));
		}
	}
}